A known art discloses a fixing structure for a vehicle interior material. As illustrated in FIG. 5, the structure includes a middle board 2, an upper board 3, and a plurality of joints 4. The middle board 2 and the upper board 3 configure a door trim 1 (an illustration of the vehicle interior material). The joints 4 join an upper end portion 2U of the middle board 2 and a lower end portion 3L of the upper board 3 together. The middle board 2 and the upper board 3 are fixed together by welding these joints 4 with a welding means such as ultrasonic welding.
However, the joints 4 of the art are arranged in a single line. Then, upon side collision of the vehicle, a body panel (not shown in the figure) located outside the compartment deforms toward the inside of the vehicle compartment and pushes the door trim 1 toward the inside of the compartment. Then, the stress is concentrated in a linear portion 5 in the lower end portion 3L of the upper board 3. Thus, when the stress concentrated in the linear portion 5 has overcome the elastic limit of the portion, the door trim 1 is damaged along the linear portion 5 as illustrated in FIG. 6. This is a possible cause of decreasing the performance of an airbag that instantly inflates in the side collision.
Thus, there is a need for a structure that can prevent concentration of the stress in the narrow area along the joints of the vehicle interior materials.